ES2638080T3 - Method for producing a flexible tube body and flexible tube body produced in this way - Google Patents

Abstract

A method of producing a flexible tube body, comprising: providing a plurality of lengths of material (7001; 7002) thermosetting compound, and stacking the plurality of lengths to form a tensile shielding element (700); helically wrap the tensile shielding element, under a predetermined tension, around a fluid retention layer (602); and then heating the tensile shielding element to cure the thermosetting composite material, in which the tensile shielding element forms a shielding layer.

Description

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DESCRIPTION

Method for producing a flexible tube body and flexible tube body produced in this way

The present invention relates to a flexible tube body and a method of producing a flexible tube body. In particular, the present invention relates to the use of composite materials, in particular fiber reinforced polymeric materials, in a shielding layer of a flexible tube body.

Traditionally, a flexible tube is used to transport production fluids, such as oil and / or gas and / or water, from one place to another. The flexible tube is particularly useful for connecting an underwater location to a sea level location. The flexible tube is generally formed as a set of a flexible tube body and one or more accessories at the ends. The tube body is typically formed as a combination of stratified materials that form a conduit that contains the pressure. The structure of the tube allows large deflections without causing deflection efforts that impair the functionality of the tube during its useful life. The tube body is generally constructed as a combined structure including metal and polymer layers.

In many known flexible tube designs, the tube body includes one or more layers of pressure shielding. The primary caga on such layers is formed from radial forces. Pressure shielding layers often have a specific cross-sectional profile to interlock so that they are able to maintain and absorb the radial forces resulting from external or internal pressure on the tube. The cross-sectional profile of the coiled wires that prevent the tube from collapsing or breaking as a result of pressure is sometimes called pressure-resistant profiles. When pressure shielding layers are formed from helically wound wires forming ring components, the radial forces of external or internal pressure on the tube cause the ring components to expand or contract, putting a tensile load on the wires .

In many known flexible tube designs, the tube body includes one or more traction shield layers. The primary burden on such a layer is tension. In high-pressure applications, such as in deep and ultra-deep water environments, the tensile shield layers experience high-tension loads from a combination of the internal load of the extreme pressure cap and the self-supporting weight of the flexible tube . This can cause a failure in the flexible tube, as these conditions are experienced for prolonged periods of time.

The unbound hose has been used for developments in deep water (less than 3,300 feet (1,005.84 meters)) and in ultra-deep waters (more than 3,300 feet). It is the growing demand for oil that is causing the exploration to take place at ever greater depths where environmental factors are more extreme. For example, in deep and ultra-deep water environments, the temperature of the ocean floor increases the risk that the production fluids are cooled to a temperature that can lead to blockage of the pipes. Increased depths also increase the pressure associated with the environment in which the hose must operate. As a result, the need for high levels of performance of the pressure shielding and tensile shielding layers of the flexible tube body is increased.

One way to improve the load response and therefore the performance of the shield layers is to make the layers of materials thicker and stronger and therefore more robust. For example, for pressure shielding layers in which the layers are often formed from coiled wires with adjacent windings in the interlacing of the layers, the manufacture of the wires with more bulky material results in the resistance being Increase properly. However, as more material is used, the weight of the flexible tube increases. Ultimately, the weight of the flexible tube can become a limiting factor for the use of the flexible tube. In addition, the manufacture of flexible tubes using bulkier and thicker material significantly increases material costs, which is also a disadvantage. The economy and logistics of transport and the installation of flexible pipes become unsustainable.

One technique that has been used in the past to somehow alleviate the aforementioned problem is the use of fiber reinforced polymeric material (or composite materials) as structural elements in flexible tubes. Composite materials provide high specific strength and stiffness and may allow reducing the weight of the tube (reducing the upper tension) and increasing the chemical resistance of the tube compared to known metallic materials. The composite material may initially be provided as a "prepreg", that is, pre-impregnated with fibers.

Thermoset composite materials that use high strength and high stiffness fibers are not ductile and cannot be plastically deformed like metals and have a limited final deformation of the order of 2% or less. Composite materials to make sections with reasonable dimensions therefore pose difficulties in the manufacturing process. A thermosetting material is defined as a material that cannot be recast after curing. A thermosetting material is the material in its uncured or partially cured state. A thermosetting composite material that has been cured is here defined as thermosetting. A thermosetting composite material can be formed on a tape and heated to cure the material. However, when the formed tape is wound to create a layer of a tube body, a tension is introduced into the

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material, which affects performance. During winding on a cylindrical base, a tape is folded into two pianos, which can cause deformation.

Document US2003 / 0026928 discloses a flexible tube that includes ribbons composed of fibers and thermosetting resin. The tape is formed by superimposed thin laminates joined together by an adhesive. The use of thin laminates helps reduce tension when the layer bends over the surface of the tube body. However, the tension is not completely eliminated, and also the thickness of the layer, the adhesive cover and the application time must be carefully controlled. Also, in use, a layer of joined laminates will be susceptible to cutting between laminates since the interfaces interact during the movement of the tube or the torsion of the layer.

WO00 / 70256 discloses a flexible high pressure light tube for applications in risers or tubena, especially at sea, comprising an internal coating, a first structural layer applied to the internal coating, to absorb pressure loads, one or more Additional structural layers applied to the first structural layer, to absorb axial and flexural loads, and an outer shell that stalls the fluids. Both the first structural layer and the additional structural layers are manufactured from a lightweight composite material consisting of a matrix reinforced with fibers, the first structural layer being a solid layer reinforced by long continuous fibers that extend around the tube and each of the additional structural layers consisting of a plurality of individual fiber-reinforced strips that extend essentially in the longitudinal direction of the strips and that are wound around the tube, but are not attached to adjacent strips or to the layers above or by under these.

US 3,531,357 discloses a machine for the continuous manufacture of a reinforced plastic tube comprising a longitudinal mandrel that extends along most of the longitudinal dimension of the machine, characterized in that said mandrel comprises a plurality of sections of a diameter that substantially corresponds to the internal diameter of the tube being manufactured, said sections being interconnected by tubular elements of smaller diameter, and which provides a relatively large diameter section of said mandrel at each winding station of bobbins of reinforcing tape, to said impregnating means and along most of the longitudinal dimension of the heating furnace, and also annular joints are provided in some of said mandrel sections.

EP2056007 discloses a flexible tube body for a flexible tube comprising an internal pressure sheath and at least one shielding layer on the sheath comprising a rolled tape of composite material. A method for manufacturing a composite tape using a pultrusion process is also disclosed.

It is an objective of the present invention to at least partially mitigate the aforementioned problems.

An objective of the embodiments of the present invention is to provide layers in a flexible tube body, of composite material that provides strength and rigidity to a tube to prevent crushing or explosion, while providing sufficient flexibility to the tube when bending.

An objective of the embodiments of the present invention is to provide shield layers in a flexible tube body of composite material that is substantially free of residual deformation.

An objective of the embodiments of the present invention is to provide a tensile shielding layer and / or pressure shielding layer that is protected against adhesion to nearby wires, abrasion and environmental factors such as temperature and chemicals.

In accordance with a first aspect of the present invention, a method of producing a flexible tube body is provided, comprising:

providing a plurality of lengths of thermosetting composite material, and stacking the plurality of lengths to form a tensile shielding element;

helically wrap the shielding element to the traction, under a predetermined tension, around a fluid retention layer;

and then heating the tensile shield element to cure the thermosetting composite material, in which the tensile shield element forms a shield layer.

According to a second aspect of the present invention, a flexible tube body formed by the method described above is provided, comprising:

a fluid retention layer; Y

at least one shield layer comprising a tensile shield element comprising a plurality of stacked lengths of thermosetting composite material, disposed on the fluid retention layer,

wherein the shielding layer is formed by helically winding the tensile shielding element, under a predetermined tension, around the fluid retention layer and then heating the tensile shielding element to cure the thermosetting material.

Certain embodiments of the invention provide the advantage that the shield layer is formed substantially or completely free of residual deformation, because the length of the material is cured "in situ", that is, it is not formed in a new position after the curing stage Certain embodiments of the invention provide a flexible tube formed with a reduced weight and improved performance compared to tubes with standard shielding layers. The composite material provides high resistance to a controlled weight. Specific materials can be chosen for the required application. It will be appreciated, however, that the present invention will be particularly suitable for operation in deep and ultra-deep waters, where the pressure on a tube is higher due to the weight of the length of a long tube, as well as the surrounding water itself and a high strength material per unit of weight is of the utmost importance.

The embodiments of the invention are described further below with reference to the accompanying drawings, in which:

15 Figure 1 illustrates a flexible tube body;

Figure 2 illustrates a riser tube assembly;

Figures 3a and 3b illustrate traction armor elements;

Figure 4 illustrates a tensile shield element in its wrapped position;

Figure 5 illustrates a pressure shielding element in its wrapped position;

20 Figure 6 illustrates an apparatus for producing a tube body;

Figure 7 illustrates an additional tensile shield element;

Figure 8 illustrates another apparatus for producing a tube body;

Figure 9 illustrates the tensile shielding element of Figure 7 which is wrapped with tape;

Figure 10 illustrates a method for producing a tube body;

Figure 11 illustrates an additional method for producing a tube body;

Figure 12 illustrates an additional method for producing a tube body; and Figure 13 illustrates an additional method for producing a tube body.

In the drawings, similar reference numbers refer to similar parts.

Throughout this description, reference will be made to a flexible tube. It will be understood that a flexible tube is an assembly 30 of a portion of a tube body and one or more accessories at the ends at each of which a respective end of the tube body is terminated. Figure 1 illustrates how the tube body 100 is formed in accordance with an embodiment of the present invention from a combination of layered materials that form a pressure-containing conduit. Although a particular number of layers is illustrated in Figure 1, it should be understood that the present invention is widely applicable to coaxial tube body structures that include two or more 35 layers made from a variety of possible materials. It should also be noted that the layer thicknesses are shown for illustrative purposes only.

As illustrated in Figure 1, a tube body includes an optional innermost shell layer 101. The housing provides an interlaced construction that can be used as the innermost layer to prevent the total or partial collapse of an internal pressure sheath 102 due to the decompression of the tube, the external pressure and the pressure of the tensile shield and loads crushing mechanics. It will be appreciated that certain embodiments of the present invention are applicable to "smooth hole" operations (ie, without a housing) as well as to such "rough hole" applications (with a housing).

The internal pressure sheath 102 acts as a fluid retention layer and comprises a polymer layer that ensures the internal integrity of the fluid. It should be understood that this layer can itself comprise a series of sub-layers. It will be appreciated that when the optional housing layer is used the internal pressure sheath is often referred to by those skilled in the art as a barrier layer. In operation without said housing (called smooth wall operation), the internal pressure sheath can be considered a lining.

An optional pressure shielding layer 103 is a structural layer with an inclination angle of approximately 90 ° which increases the resistance of the flexible tube to internal and external pressure loads and mechanical crushing.

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The layer also structurally supports the internal pressure sheath, and typically consists of an interlaced construction.

The flexible tube body also includes an optional first tensile shield layer 105 and an optional optional tensile shield layer 106. Each traction shielding layer is a structural layer with an inclination angle typically between 10 ° and 55 °. Each layer is used to sustain tensile loads and internal pressure. Traction shield layers are often rewound in pairs.

The flexible tube body shown also includes optional layers of tape 104 that help contain underlying layers and, to some extent, prevent abrasion between adjacent layers.

The flexible tube body also typically includes optional insulation layers 107 and an outer sheath 108 comprising a polymer layer used to protect the tube from penetration of seawater and other external environments, corrosion, abrasion and mechanical damage.

Each flexible tube comprises at least one part, sometimes referred to as a segment or section of the tube body 100 together with an end fitting located at least at one end of the flexible tube. An end fitting provides a mechanical device that forms the transition between the flexible tube body and a connector. The different tube layers, as shown, for example, in Figure 1, are terminated in the end fitting such that the load is transferred between the flexible tube and the connector.

FIG. 2 illustrates an ascending tube assembly 200 suitable for transporting production fluid such as oil and / or gas and / or water from an underwater position 201 to a floating installation 202. For example, in Figure 2, the underwater position 201 includes an underwater flow line. The flexible flow line 205 comprises a flexible tube, in whole or in part, which rests on the seabed 204 or is buried under the seabed and is used in a static application. The floating installation can be provided by a platform and / or a buoy or, as illustrated in Figure 2, a ship. The ascending assembly 200 is arranged as a flexible conduit, that is to say a flexible tube 203 that connects the vessel to the seabed installation. The flexible tube may be in flexible tube body segments with connection connectors.

It will be appreciated that there are different types of riser, as is well known to those skilled in the art. The embodiments of the present invention can be used with any type of ascending tube, such as a freely suspended ascending tube (free ascending tube, or catenary), a vertical tube held to a certain extent (buoys, chains), fully contained or enclosed in a tube (tubes I or J).

Figure 2 also illustrates how flexible tube portions can be used as a flow line 205 or a bridge 206.

Figures 3a and 3b illustrate an example of an element for forming a tensile shield layer. Element 300-1 or 3002, which in the art may be referred to as tape, includes a composite matrix material 302 and reinforcing fibers 304. The relative dimensions, the shape of the cross section and the relationship of the matrix material with the fibers are illustrated, for example, and can be made to adapt them to the particular application. The cross-sectional shape of the element may be substantially rectangular, substantially oval, substantially circular, etc., or it may be made of two or more corresponding pieces, or any other cross-section.

One or more elements form a tensile shield layer by helical wrap of the element around a radially internal layer, such as in the form shown in Figure 4. In a typical use, the tensile shield elements are wound with an inclination angle of 10 to 55 °. Alternatively, when the invention is directed to a shielding layer at the pressure of a flexible tube body, the shielding element can be wound with an angle of inclination close to 90 °, as shown in Figure 5.

The matrix composite material 302 is, in this example, the epoxy resin and the reinforcing fibers 304 are carbon fibers. The composite material of matrix material and fibers can be obtained in prepreg form from Zoltek Companies, Inc. This prepreg is available in a partially cured state, the curing being chemically delayed to allow a simple manipulation, a continuous prepreg material with a tension distribution uniform and minimal on the material. The ratio of matrix to fiber (volumetric fraction of the fibers) is around 50%. However, many thermosetting prepreg materials may be suitable such as thermosetting, polyimides, bismaleimides, phenolics and modified epoxies. The reinforcing fibers could be any suitable fiber such as glass, ceramic, metal, polymeric fibers such as aramid, or mixtures thereof. The volumetric fraction of the fibers could be any amount of about 40% to about 75%, appropriately about 40% to 65%. The composite material may also include other modifiers such as pigments or plasticizers. Appropriately, most of the reinforcing fibers are oriented longitudinally along the longitudinal axis of the tensile shielding element. Some transverse or angular fibers can be included to help stabilize the structure. For example, more than 50%, or 60%, or 70%, or 80% or 90%, of the fibers can be aligned in a substantially axial direction with the length of the material. Such orientation can help stabilize the shield element during use.

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Figure 6 shows the apparatus 600 for producing a flexible tube body that includes the tensile shielding element shown in Figures 3a and 4.

To produce a flexible tube body, a length of the shield element 300 to the prepreg composite pull is fed into a fluid retention layer 602. Optionally, an extrafole mandrel could be used as a more internal base to apply layers circumferentially to it. The fluid retention layer 602 is rotated clockwise if viewed from the left side as shown, and at a suitable predetermined rotation speed. The fluid retention layer 602 also moves at a constant predetermined speed in a direction shown by the arrow A. Of course, alternatively, the length of the traction armor element could rotate around a stationary fluid retention layer.

The traction shielding element 300 passes through a grille 604 and a preheater 606 in this embodiment (although these features of the apparatus are optional). The grind 604 helps to correctly position the element 300 and the preheater 606 helps to slightly soften the prepreg material for application on the fluid retention layer 602.

The traction shielding element 300 is then applied to the fluid retention layer 602, which is wrapped around the fluid retention layer 602 by virtue of the rotation of the layer 602, the linear translation of the layer 602 and of the fixed position of the supply 601 of the shielding element to the traction. Element 300 feeds the fluid retention layer under a constant predetermined controlled tension of 100N. The tension can be altered on a case-by-case basis to adapt to the materials and dimensions of the shield element. The predetermined voltage is greater than zero, and perhaps between 50 to 1000N, for example, 50 to 150N, 50 to 250N or 50 to 500N, for example.

Although only one feed of shield element 601 is shown, other feeds can be used to allow other shield elements to be wound on the tube body. Other shielding elements will increase the number (and relative density) of the shielding elements in the layer. An adequate number of elements can be chosen so that the elements have sufficient clearance not to overlap and scrape each other, but provide sufficient tension support to the flexible tube. It will be appreciated that an additional layer of the tensile shield elements could be provided on the first layer of tensile shield elements by counter winding elements in the direction opposite to the first layer, for example.

The positioning head 608 helps position the element 300 on the fluid retention layer 602.

As the tensile shielding element is wound on the tube body, the tube body continues to move in a linear direction (arrow A) and the tube body moves through an oven 610.

The oven 601 is set at 220 ° C to start curing the epoxy resin of the shielding element 300, although it will be clear that other temperatures may be chosen, which will affect the epoxy curing time and, therefore, the speed at which the tube body must travel through the oven.

In this embodiment, the thermosetting material hardens in the heating zone by the oven. It will be apparent that the thermosetting material could be cured alternately in other ways, such as by application of other forms of radiation, or chemically cured.

Such "in situ" curing of the composite material of the shielding layers allows a shielding layer to be formed substantially or completely free of residual deformation within the material, because the material does not significantly bend or reshape after curing. The radius of curvature and torsion occur when the material is in its pre-cured state (which does not affect the material) and no torsional or flexural tension is applied to the post-cured material. This gives a higher quality product compared to the known shield layers, since the shield element contains more usable resistance than the known shield elements that contain residual stress. The product is more efficient than the known shielding layers in terms of resistance by amount of material and, therefore, a longer tube is possible for a deeper application.

By winding the shielding element to the traction under a controlled tension, the element receives an amount of consolidation pressure through the mutual radial forces acting between itself and the fluid retention layer. This pressure helps the curing process.

A user may consider any contraction of the thermosetting material by arranging the positioning of the shielding elements with respect to each other.

Figure 8 shows apparatus for producing a flexible tube body according to the present invention. The equipment shown in Figure 8 is similar to the equipment shown in Figure 6. However, a variation of the tensile shielding element is used, as shown in Figures 7 and 9.

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A plurality of lengths of composite material is stacked to form a tensile shield element. The precursor lengths can be cut from a sheet of composite prepreg material that is available from Zoltek Companies, Inc., and then stacked side by side in a laminated manner.

Appropriately, substantially all reinforcing fibers are oriented longitudinally along the longitudinal axis of the tensile shield element. Such orientation can help stabilize the shield element during use. By orienting the fibers in particular directions and / or angles, the spring stiffness of the element can be controlled.

In one embodiment, the tensile shielding element also includes a heat shrink tape that covers and encapsulates the stacked lengths of composite material. The shrink tape itself is a known material, which is a polymeric tape that has been previously treated by heating and stretching in a particular direction giving the tape an oriented shape with oriented polymer chains. The application of heat reverses the process, causing the tape to move back to its original position. The "Shrink Tite" tape available at Aerovac Systems Ltd. can be used.

A heat shrink sleeve or braided tube sleeve could be used to encapsulate the composite. However, in this embodiment a heat shrink tape is wound on the stacked composite with an overlap of approximately 50%.

The method of producing a flexible tube body is similar to the method described with respect to Figure 6. However, the method also includes the initial steps of stacking the lengths of composite material 7001, 7002, to form the shielding element to the traction, and wrapping the heat shrink tape 702 around the stack 700. This wrapping stage can be mechanically performed through winding means. The rest of the apparatus 800 operates in the same manner as the apparatus 600 and is operated by the same method as described above.

Figure 9 illustrates the winding means 902 in more detail.

By forming the tensile shielding element 700 from a stack of elements cut from a flat sheet, the initial alignment of the reinforcing fibers can be controlled more carefully and, therefore, more uniformly oriented on a sheet flat. The fibers remain uniformly oriented in the stack.

In addition, by using a stack of elements, the prepreg material is not stretched or damaged during flexion in the wrapping stage on the fluid retention layer. However, the requirement of very thin layers of composite material is avoided (as needed in the prior art).

The heat shrink tape works to compress the prepreg a certain amount, thus applying a consolidation pressure to the prepreg material. This pressure helps the curing process similar to the pressure of winding the armor element under tension. The heat shrink tape could be used instead or as a winding under tension.

In addition, the consolidation pressure of the heat shrink tape also helps to create an excellent bond between the stacked layers of composite material during the curing process, giving a unique consolidated thermosetting element after curing.

In addition, the heat shrink tape can be used as a protective layer for the shielding element, preventing nearby elements from joining during the curing process. This ensures the free movement of the shielding elements when the entire structure is subject to flexion during use. The layer of heat shrink tape can also provide a degree of protection against abrasion between individual wires and an additional layer of protection against the penetration of fluids present in the tube ring forming a barrier to physical permeability. In an alternative embodiment, the heat shrink tape may be removed after the curing stage.

Because the shielding element is cured "in situ" as in the first embodiment, the same advantages are also achieved, that is, a lack of residual tension in the shielding layers formed.

Both the tensile shield and the pressure shield can be formed continuously by this method, and the cross section of the element can be chosen to adapt it to the functional layer. For example, the pressure shielding element may have a Z-shaped cross section, which allows the element to interconnect with nearby sections of the element.

With the present invention, the prepreg composite material can be wrapped around an inner layer of tube body, or a mandrel, with low tension, requiring only quite basic rotating machinery.

A method for producing a flexible tube body is illustrated in the flowchart of Figure 10. An additional method is illustrated in the flowchart of Figure 11. Another additional method is illustrated in the flowchart of Figure 12. Another additional method is illustrated in the flowchart of Figure 13.

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Various modifications of the detailed designs are possible as described above. For example, the heat shrink tape of Figure 7 could be modified to include PTFE tape or other low friction material, particularly on the surface, in order to improve the friction properties between adjacent elements or adjacent layers. One or more additional layers can be added to the flexible tube body, such as the 5 illustrated in Figure 1.

Claims (16)

5 10 fifteen twenty 25 30 35 40 Four. Five 1. A method for producing a flexible tube body, comprising: providing a plurality of lengths of material (7001; 7002) thermosetting compound, and stacking the plurality of lengths to form a tensile shielding element (700); helically wrap the shield element to the traction, under a predetermined tension, around a fluid retention layer (602); and then heating the tensile shield element to cure the thermosetting composite material, in which the tensile shield element forms a shield layer. 2. A method as claimed in claim 1, wherein the thermosetting composite material comprises a thermosetting matrix material (302) and a plurality of reinforcing fibers. 3. A method as claimed in claim 2, wherein more than 50% of the plurality of reinforcing fibers are aligned in an axial direction with the length of the material. 4. A method as claimed in any of the preceding claims, wherein the shielding layer is substantially free of residual deformation. 5. A method as claimed in any of the preceding claims, wherein the predetermined voltage is in the range of 100 N to 1000 N. 6. A method as claimed in any one of the preceding claims, wherein the helical wrapping step comprises helically wrapping the shielding element to the traction so that adjacent sections of the wrapped material do not overlap or, helically wrap the shielding element to the traction so that adjacent sections of the at least partially wrapped material overlap. 7. A method as claimed in any of the preceding claims, further comprising the step of applying a heat shrink tape (702) or a heat shrink sleeve to the length of thermosetting composite material before the helical wrapping stage. 8. A method as claimed in claim 7, wherein the heat shrink tape or heat shrink sleeve comprises a low friction material. 9. A flexible tube body formed by the method of any preceding claim, comprising: a fluid retention layer (602); Y at least one shielding layer comprising a tensile shielding element (700) comprising a plurality of stacked lengths of thermosetting composite material (7001; 7002), provided on the fluid retention layer, wherein The shield layers are formed by helically wrapping the tensile shielding element, under a predetermined tension, around the fluid retention layer and then heating the tensile shielding element to cure the thermosetting material. 10. A flexible tube body as claimed in claim 9, wherein the thermosetting composite material comprises thermosetting matrix material (302) and a plurality of reinforcing fibers (304). 11. A flexible tube body as claimed in claim 10, wherein more than 50% of the plurality of reinforcing fibers are aligned in an axial direction with the length of the material. 12. A flexible tube body as claimed in any of claims 9 to 11, wherein the shielding layer is substantially free of residual deformation. 13. A flexible tube body as claimed in any one of claims 9 to 12, wherein the predetermined tension is in the range of 100 N to 1000 N. 14. A flexible tube body as claimed in any one of claims 9 to 13, in which adjacent sections of the wrapped material do not overlap or in which adjacent sections of the wrapped material overlap at least partially. 15. A flexible tube body as claimed in any one of claims 9 to 14, further comprising a heat shrink tape (702) or a heat shrink sleeve over the length of thermosetting composite material. 16. A flexible tube body as claimed in claim 15, wherein the heat shrink tape or the heat shrink sleeve comprises a low friction material.